1. Field of the Invention
This invention relates to an exhaust switch-over valve malfunction detection system of an internal combustion engine with an exhaust gas purification system that includes an adsorber (stored in a bypass branched from the exhaust pipe that is opened/closed by a swtich-over valve) which adsorbs unburned components such as the hydrocarbon (HC) content of the exhaust gas generated by the engine. This enhances exhaust gas purification, more particularly the invention acts as a system for detecting switch-over valve malfunctions provided at the branching point to selectively open/close the bypass.
2. Description of the Related Art
Internal combustion engines are ordinarily provided with a catalyst (a three-way catalytic converter) in the exhaust system which removes HC, NOx and CO components in the exhaust gas generated by the engine. However, when the engine is cold started, for example, and the catalyst is not activated, unburned components of the exhaust gas, in particular, unburned HC are relesed immediately into the atmosphere.
For that reason, an exhaust gas purification system is proposed, in which the exhaust pipe is branched out at a location downstream of the catalyst and the bypass is provided with an adsorbent made of a zeolite material or some similar materials which adsorbs unburned components such as the HC content when the catalyst is not activated and desorbs the same after the catalyst has been activated to be recirculated into the engine intake system and burned again in the combustion chambers. The bypass is opened/closed by a switch-over valve.
No exhaust gas purification can be achieved in this kind of system if the switch-over valve malfunctions, Japanese Laid-Open Patent Application No. Hei 10 (1998)-159,544 discloses the technique to detect malfunctions of the switch-over valve.
In this prior art, a temperature sensor is installed downstream of the adsorber to detect the temperature Tb at that location if the engine is discriminated to be under steady-state (idling) when the bypass is closed, and then to detect the temperature Ta at the same location if the engine is discriminated to be under steady-state when a time td has passed since the opening of the valve. Then, the difference between Ta and Tb is calculated and it is compared to a predetermined value .DELTA.Tlo.
If the result of the Ta and Tb difference is less than or equal to .DELTA.Tlo is it is determined that the valve leaks.
Moreover, in this prior art, the temperature sensor detects the temperature T3c at the time when a recirculation conduit (which allows the desorbed unburned component to be recirculated upstream) is closed, then another temperature T3d at the same location is detected if the engine is discriminated to be under steady-state (idling) when the recirculation conduit is closed. The difference between T3d and T3c is then calculated and it is determined whether the difference is less than or equal to a predetermined value .DELTA.T3o. When the result is negative, it is also determined that the valve leaks.
In this prior art, thus, the temperatures are detected when the switch-over valve is closed and opened during the engine steady-state. Since, however, the detections are conducted at different times, the engine operation, if it is under steady-state, may be different, in precise speaking, from each other in between these detection times, rendering the malfunction detection accuracy degraded.